Patient-level outcomes are the ultimate indicators of the effectiveness of mental health interventions. Patient-reported outcomes, such as subjective well-being and quality of life, are increasingly recognized as integral to quality care. Nonetheless, evidence of intervention effectiveness is based primarily on objective outcomes, such as decreased hospitalization and increased community tenure. Even psychometrically sound measures of subjective, patient-reported outcomes have tended to yield inconclusive findings. These disappointing results signal discrepancies between objective and subjective outcomes that limit the field's ability to distinguish differentially effective interventions. Self-assessments of symptoms, distress and well-being are complex, encompassing multiple cognitive tasks. Difficulties with one or more of these tasks can reduce the accuracy, validity and reliability of outcome measurement and the types of difficulties encountered can vary across diagnostic groups. Theory and evidence on cognitive aspects of measurement, cognition and mental illness and subjective well-being combine to provide a promising framework for exploring the levels of cognition involved in measuring subjective outcomes. The proposed exploratory study will begin to examine a cognitively based paradigm for selecting and developing standardized measures of patient-reported outcomes that capture key aspects of intervention impact in community care settings. A three-phase mixed methods study will analyze existing quantitative data and collect and analyze additional quantitative and qualitative data from clients in two treatment programs that have hosted practice-based clinical trials. Analyses will explore the roles of five levels of cognition hypothesized to affect measurement quality (comprehension, recollection, adaptation, salience and preference) and evaluate alternative measurement methods that address identified cognitive difficulties. Results will inform selection of available outcome measures and will define a focused research agenda for developing of improved measures of subjective, patient-reported outcomes that can facilitate the identification and dissemination of effective mental health interventions.